“Never before has there been such a clear need for science to be at the service of a new global ecological equilibrium,” the pope said, addressing the Vatican’s academy of sciences on Monday. He spoke of the world “threatened…by ecological collapse” and the need to “develop a cultural model which can face the crisis of climatic change and its social consequences.”

It was one of the pope’s strongest speeches yet on the environment. And it took place just weeks after Donald Trump, a vocal climate change skeptic, won the U.S. presidential election. Trump, who has called climate change an “expensive hoax,” pledged on the campaign trail to roll back U.S. environmental pledges with the idea of somehow reinvigorating an ailing U.S. coal sector. The U.S. Republican Party is one of the only major political formations on the planet that does not believe in man-made climate change.

In contrast, U.S. leadership under President Barack Obama was critical to brokering a landmark international climate change deal last December. Trump could pull the United States out of that deal once in office, as Foreign Policy reported.

Hence the papal pleas — and criticisms — on Monday. The head of the Catholic church (a scientist himself) castigated climate change deniers and “the ease with which well-founded scientific opinion about the state of our planet is disregarded.” The proof of this, the pope said, was the “‘distraction’ or delay in implementing global agreements on the environment.”

The pope has garnered international attention for his outspoken views on climate change in the past. In May 2015, he released a first-of-its-kind encyclical on the moral obligations of combating climate change. In his encyclical on ecology, the pope explicitly stated that climate change stemmed “mainly as a result of human activity.”

But the Pope’s environmental messages haven’t appeared to budge Trump. On Sunday, Trump’s incoming White House Chief of Staff Reince Priebus dispelled rumors of his new boss changing his mind on climate change.

“He’ll have an open mind about it but he has his default position, which most of it is a bunch of bunk,” Priebus told Fox News Sunday.